1. Field of the Invention
The present invention relates to an imaging apparatus, an auto-focusing method and a recording medium.
2. Description of the Related Art
For example, Japanese Patent Application Laid-Open (Kokai) Publication No. 2006-352716 discloses a technology in which, in an imaging device such as a charge-coupled device (CCD), 2-pixel addition or 4-pixel addition is performed on information of pixels arrayed in a vertical direction to improve imaging performance in dark environments.
However, in the technology described in Japanese Patent Application Laid-Open (Kokai) Publication No. 2006-352716, pixel addition is performed only in the vertical direction. Therefore, sufficient improvement of imaging performance in a dark environment may not be expected depending on an image composition (how a camera is held, and whether an image is imaged horizontally or vertically) when contrast-based auto-focusing is performed.
In general, subjects, such as humans, often include vertical contour lines rather than horizontal contour lines. To successfully perform contrast-based auto-focusing operations in a dark environment on a subject such as this, numerous vertical line components constituting the subject are required to be detected with high contrast.
For example, in an ordinary image composition in which the camera is held horizontally (referred to, hereinafter, as a horizontal imaging), as a result of “vertical pixel addition”, pixel addition readout is performed on vertical-direction pixels information having few contrast components to brighten an image. Information of the horizontal-direction pixels including numerous information (contrast components) required to perform auto-focusing (AF) is readout from all pixels. As a result, the vertical contour lines included in the subject are detected with high contrast, allowing auto-focusing operations to be successfully performed.
However, in the technology described in Japanese Patent Application Laid-Open (Kokai) Publication No. 2006-352716, pixel addition is performed only in the vertical direction. Therefore, in an image composition in which the camera is held vertically (referred to, hereinafter, as a vertical imaging), the contour lines included in the subject and the pixel addition direction match, and as a result, pixel addition readout is performed on the vertical-direction pixel information including numerous information (contrast components) required to perform AF. Accordingly, there is a problem in that, although the image is brightened, the contour lines included in the subject are not detected with high contrast.